JP4787941B2 - Method for producing thermoformable foam sheet using physical foaming agent - Google Patents

Method for producing thermoformable foam sheet using physical foaming agent Download PDF

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JP4787941B2
JP4787941B2 JP2001557948A JP2001557948A JP4787941B2 JP 4787941 B2 JP4787941 B2 JP 4787941B2 JP 2001557948 A JP2001557948 A JP 2001557948A JP 2001557948 A JP2001557948 A JP 2001557948A JP 4787941 B2 JP4787941 B2 JP 4787941B2
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sheet
foam
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molten
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JP2003522052A (en
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シー ウエルシュ，ゲリー
ジェイ サルマング，ロルドルフォ
エム バロット，マイケル
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Dow Global Technologies LLC
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
    • C08J9/122—Hydrogen, oxygen, CO2, nitrogen or noble gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/56—After-treatment of articles, e.g. for altering the shape
    • B29C44/5627—After-treatment of articles, e.g. for altering the shape by mechanical deformation, e.g. crushing, embossing, stretching
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/02—Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
    • C08J2201/03—Extrusion of the foamable blend
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/06—CO2, N2 or noble gases
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2325/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Derivatives of such polymers
    • C08J2325/02—Homopolymers or copolymers of hydrocarbons
    • C08J2325/04—Homopolymers or copolymers of styrene

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  • Extrusion Moulding Of Plastics Or The Like (AREA)
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  • Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は二酸化炭素、水及び／又は窒素等の物理発泡剤を用いる発泡体の製造方法に関する。
【０００２】
【従来の技術とその課題】
スチレン系及びオレフィン系ポリマーは乳製品用容器に用いる非発泡性熱成形性シート等の食品包装用途に用いられている。このタイプの熱成形性シートは、典型的には、ポリマーをフラットシートダイから３ロール磨きスタック上に押し出してから巻き取るか又は直接熱成形プロセスに供給するという一般的なシート押し出しラインを用いてつくられている。しかし、包装した食品処理機に供するときの費用が包装重量に依存することもありより軽い包装材料を製造することが食品包装分野で一層求められている。
【０００３】
熱成形性シートの重量を減らす一つの方法は発泡剤を入れて高密度の発泡体シートをつくることである。このタイプの発泡体シートは典型的には一般的なシート押し出しラインと化学発泡剤を用いて製造される。しかし化学発泡剤は高価であると共に一定で均一な発泡がむずかしく、得られた発泡体シート内に発泡体のゲージと密度の変動をもたらす。
それ故、高密度発泡した包装材料、特に一定のゲージと密度をもち、乳製品等の古くからの非発泡体用途にも用いうる熱成形性発泡体シートの製造方法の開発が依然求められている。
【０００４】
【課題を解決するための手段】
本発明は溶融したモノビニリデン芳香族又はオレフィン系ポリマーを物理発泡剤と接触させてシート押し出しライン内でポリマー／発泡剤混合物を形成し、この混合物をより低圧の領域中に発泡させて発泡している押し出し物をつくり、そしてこの発泡している押し出し物を引っ張りそして圧縮して３ｍｍ未満の均一な厚さをもつ発泡体シートを形成することを特徴とする熱可塑性発泡体シートの製造方法である。
【０００５】
本発明はまた上記の方法で製造した熱可塑性発泡体シート及びそれから製造した熱成形物品も包含する。
本発明の方法は高密度発泡した包装材料、特に一定のゲージと密度をもち、乳製品等の古くからの非発泡体用途にも用いうる熱成形性発泡体シートの製造に特に適している。
【０００６】
【発明の実施の形態】
図１は本発明の方法で用いるシート押し出しラインの一態様を示す概略図である。樹脂及び任意成分の核剤（II）を混合ヘッド（III)、静止ミキサー（IX）、ギアポンプ（VIII）及びダイ（Ｘ）をもつ押し出し機（Ｉ）に供給する。そこでリリーフ機構（Ｖ）をもつ容積移送式真空ポンプ（IV）に接続した保存タンク（VI）から、物理発泡剤を押し出し機の射出弁（VII)を通して射出する。発泡体シートを引っ張り３ロール磨きスタック（XI）中に圧縮しそして巻き上げて発泡シートの巻き上げ体（XII)を形成する。
【０００７】
本発明で有用な熱可塑性ポリマーには、ポリエチレン、ポリプロピレン、線状低密度ポリエチレン、低密度ポリエチレン、高密度ポリエチレン、エチレン−オクテンコポリマー等のオレフィン系コポリマー、最終樹脂中に少なくとも７０重量％のビニル芳香族モノマーをモノマー反復単位として含有させたポリマー、コポリマー及びインターポリマー等が包含される。ビニル芳香族モノマーの非限定的な例は米国特許第４，６６６，９８７号，４，５７２，８１９号及び４，５８５，８２５号に記載されている。
【０００８】
好ましいこれらのモノマーは式：

Figure 0004787941
（ここでＲ’は水素又はメチルであり、Ａｒは１〜３個の芳香族環をもつ芳香族環構造であり、これにはアルキル、ハロゲン又はハロアルキルが置換していてもよく、ここでアルキル基は１〜６個の炭素原子をもち、ハロアルキルはハロゲン置換アルキルを意味する、で示されるモノマーである。好ましくはＡｒはフェニル又はアルキルフェニルであり、ここでアルキルフェニルはアルキル置換フェニル基を意味する。フェニルが最も好ましい。用いうる代表的なビニル芳香族モノマーの例としては、スチレン、アルファメチルスチレン、ビニルトルエンの全異性体、特にパラビニルトルエン、エチルスチレンの全異性体、プロピルスチレン、ビニルビフェニル、ビニルナフタレン、ビニルアンスラセン及びそれらの混合物がある。ビニル芳香族モノマーは他の共重合性モノマーと合体してもよい。これらのモノマーの非限定的な例としては、アクリロニトリル、メタクリロニトリル、メタクリル酸、メチルメタクリレート、アクリル酸、メチルアクリレート、マレイミド、フェニルマレイミド及び無水マレイン酸がある。またビニル芳香族モノマーの重合を予め溶解させたエラストマーの存在下に行って衝撃変性又はグラフトゴム含有生成物をつくることもでき、これらは米国特許第３，１２３，６５５号、３，３４６，５２０号、３，６３９，５２２号及び４，４０９，３６９号に記載されている。特に好ましいのは高衝撃ポリスチレン樹脂である。また本発明の方法では上記した適宜のポリマーのブレンド物や組合せも用いうる。
【０００９】
本発明の方法に用いる発泡剤は適宜の物理発泡剤であり、その非限定的な例としては二酸化炭素（ＣＯ2 ）、窒素（Ｎ2 ）、水（Ｈ2 Ｏ）又はそれらの組合せがある。本発明では、これらの物理発泡剤は、少量の不純物や小量の他の化合物を含有しうるとしても、化学発泡剤が存在しない実質上１００％の物理発泡剤として定義されうる。好ましい発泡剤は１００％の二酸化炭素である。
【００１０】
物理発泡剤は適宜の状態で用いうるが、好ましくは気体又は液体である。二酸化炭素は好ましくは液体としてポリマー溶融物に加えられる。しかし本発明では二酸化炭素ガスも用いうる。窒素や水も適宜の状態で用いうるが、好ましくは窒素は気体として、また水は液体として加えられる。２種以上の組合せや混合物を用いる場合には、典型的には、別々の計量系を用いてキャスト−押し出しプロセスの射出点の前に多重流が合体するようにする。しかし複数の発泡剤を予め混合して単一計量系を用いて射出することもできる。
【００１１】
顔料及び／又は核剤等の添加剤も本発明の方法において用いうる。核剤の添加は一般に好ましく、また好ましくは全ポリマーの０．００１〜１０重量％添加される。核剤のより好ましい添加量は０．０２〜２重量％である。核剤は典型的には押し出し機中でポリマーに添加される。一の態様における核剤はタルクである。
【００１２】
本発明の方法は共押し出し技術を利用して多層発泡体シートをつくることもできる。これらの多層シートは所望により１以上の発泡コア層又は発泡スキン層をもちうる。ある種の用途では、１以上の発泡コア層又はスキン層と非発泡コア層又はスキン層との組合せとすることが望ましい。たとえば、一の態様では、非発泡高衝撃ポリスチレン又は非発泡ポリスチレン樹脂／高衝撃ポリスチレン樹脂からなる外側スキン層をもつ発泡ポリスチレンコア層からなる多層共押し出しシートがつくられる。共押し出し法は当該分野で周知である。
【００１３】
シート押し出しは当該分野で周知であり、１９８８年にニューヨークのＨａｎｓｅｒ Ｐｕｂｌｉｓｈｅｒｓが発行したＦ．Ｈｅｎｓｅｎ著Ｐｌａｓｔｉｃｓ Ｅｘｔｒｕｓｉｏｎ Ｔｅｃｈｎｏｌｏｇｙ，７編２０３−２５１頁及び１９８９年１０月中旬発行のＭｏｄｅｒｎ Ｐｌａｓｔｉｃｓ Ｅｎｃｙｃｌｏｐｅｄｅｉａ Ｉｓｓｕｅ，６６巻、Ｎｏ．１１、２５６〜２５７頁に記載されている。
【００１４】
本発明で用いるシート押し出し法はポリマーをシート押し出し機に供給して溶融し、そこで溶融物を任意のフィードブロックに移し、ダイを通してダイ出口で均一厚さの単層又は多層押し出し物（シート）を得るものである。本発明の方法におけるダイでの発泡温度は発泡すべきポリマーに依存し、典型的には１５０℃以上、好ましくは１７０〜３００℃である。ポリマー／発泡剤混合物を低圧領域に好ましくは大気圧下の空気中に押し出して発泡させる。押し出された発泡体シートを均一厚さのシートが得られるように発泡押し出し物を引っ張り圧縮する機構に引き入れる。このような機構の一つに回転可能で、温度制御した３ロール磨きスタック（ｐｏｌｉｓｈｉｎｇ ｓｔａｃｋ）がある。この機構では、シートのゲージは押し出し速度、ロールスタック間隔、ライン速度及びドロー比によって決まる。ロールスタック間隔は下方向に配置して用いる場合の３ロール磨きスタックの上部ロールと中間ロール間の間隔である。シートのゲージはシート方向と垂直に動きシートを横切ってゲージ機器を運ぶカートリッジ上に配した機器によってモニターされる。このようなゲージ機器は当該分野で周知である。シートはこれらの計量領域を出て一連のガイドローラー上を移動し、必要に応じて設けたスリット領域及び巻き取り機へ又は直接熱成形プロセスへと移動される。
【００１５】
本発明の方法はまた物理発泡剤をシート押し出し機のダイより前の位置でポリマー溶融物に導入する点にも特徴がある。好ましくは、シート押し出しライン内の押し出しスクリューの圧縮解放領域（ベントポート）に配した一方向弁を介して発泡剤を射出する。所望により、ポリマーを発泡剤及び核剤（用いる場合）と混合するためにダイより前に静止ミキサーを配しうる。発泡はポリマー溶融混合物がダイから出次第ダイ出口直前から低圧領域で起こって続く。典型的には、非発泡材料又は化学発泡高密度発泡体シートを押し出すのにシート発泡法が用いられる。物理発泡剤と前記したシート押し出しラインを用いることで、改良されたゲージ均一性と密度均一性をもつ高密度発泡体シートを製造できることを見出した。
【００１６】
得られる発泡体シートは、典型的には、２５〜６５ポンド／立方フィート（ＰＣＦ）（４００〜１０５０ｇ／Ｌ（リットル））、好ましくは４５〜５５ＰＣＦ（７２５〜８９０ｇ／Ｌ）の範囲の密度をもち、ポリマー重量当たり０．０４〜１重量％、好ましくは０．０４〜０．５重量％の物理発泡剤が用いられる。本発明の方法において水をポリマー重量当たり０．２重量％より少量用いると水は冷却剤として機能しポリマーの膨張はもたらさない。この冷却効果は発泡構造物の発泡速度の制御にとって有効である。０．２重量％より多量に用いるとポリマー溶融混合物の発泡が認められる。全方向での発泡シートのセル寸法は１ｍｍ以下、好ましくは０．５ｍｍ以下である。発泡体シートの厚さは好ましくは０．１〜３ｍｍである。
【００１７】
得られる発泡体シートは改良されたゲージ均一性と密度均一性をもつ。最終シートの平均厚さに対する最終シートの適宜の位置の厚さを比較することでゲージ均一性を求めることができる。比較すると２つの厚さの違いは６％より小さい。密度均一性は最終シートの平均シート密度に対する最終シートの適宜の位置の密度を比較することで求めることができる。比較すると２つの密度の違いは４％より小さい。換言すると、最終シート上で測定したゲージはどこでも平均シートゲージから６％と違っていずまた最終シート上で測定した密度はどこでも平均密度から４％と違っていない。
【００１８】
次の例は本発明を例証するものである。これらの例は本発明の範囲を制限するものではない。量は特に断りのない限り重量％で示す。
【００１９】
【実施例】
実施例１：
３２０，０００のＭｗをもつ汎用のポリスチレン樹脂をベントポート位置に高圧ピストンポンプをもつシート共押し出しラインに供給し、そこで発泡剤として１００％ＣＯ2 を押し出しバレルに計量して導入した。押し出し機端にはポリマー／発泡剤混合物の混合を改善するために静止ミキサーも配した。同時にポリスチレン樹脂と衝撃変性ポリスチレン樹脂の５０／５０ブレンド物を、共押し出し固形スキン層の形成用に、発泡剤なしの別のシート押し出しラインに供給した。ポリスチレン樹脂を発泡させ、非発泡ポリスチレン／ＨＩＰＳブレンド物と共押し出しして発泡コア樹脂とこのコア樹脂層の両側に接着した固形スキン２層をもつシートをつくった。このシートを引っ張り３ロール磨きスタックによって圧縮した。プロセス条件とシートの特性を次表に示す。
【００２０】
Figure 0004787941

【図面の簡単な説明】
【図１】 本発明の方法で用いるシート押し出しラインの一態様を示す概略図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a foam using a physical foaming agent such as carbon dioxide, water and / or nitrogen.
[0002]
[Prior art and its problems]
Styrenic and olefinic polymers are used in food packaging applications such as non-foaming thermoformable sheets used in dairy containers. This type of thermoformable sheet is typically made using a common sheet extrusion line in which the polymer is extruded from a flat sheet die onto a three roll polishing stack and then wound or fed directly into the thermoforming process. It has been. However, there is a further demand in the field of food packaging to produce a lighter packaging material because the cost of supplying the packaged food processing machine depends on the weight of the packaging.
[0003]
One way to reduce the weight of the thermoformable sheet is to add a blowing agent to make a dense foam sheet. This type of foam sheet is typically manufactured using common sheet extrusion lines and chemical blowing agents. However, chemical blowing agents are expensive and difficult to achieve uniform and uniform foaming, resulting in foam gauge and density variations within the resulting foam sheet.
Therefore, there is still a need to develop a method for producing a thermoformable foam sheet that can be used for high-density foam packaging materials, particularly dairy products that have a constant gauge and density, and can be used for old non-foam applications such as dairy products. Yes.
[0004]
[Means for Solving the Problems]
The present invention involves contacting a molten monovinylidene aromatic or olefinic polymer with a physical blowing agent to form a polymer / foaming agent mixture in a sheet extrusion line, and foaming the mixture by foaming into a lower pressure region. A method for producing a thermoplastic foam sheet, characterized in that an extrudate is produced and the foamed extrudate is pulled and compressed to form a foam sheet having a uniform thickness of less than 3 mm. .
[0005]
The present invention also includes a thermoplastic foam sheet produced by the above method and a thermoformed article produced therefrom.
The method of the present invention is particularly suitable for the production of high density foamed packaging materials, particularly thermoform foam sheets that have a constant gauge and density and can be used in traditional non-foam applications such as dairy products.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view showing an embodiment of a sheet extrusion line used in the method of the present invention. The resin and the optional nucleating agent (II) are fed to an extruder (I) having a mixing head (III), a static mixer (IX), a gear pump (VIII) and a die (X). Therefore, the physical foaming agent is injected from the storage tank (VI) connected to the positive displacement vacuum pump (IV) having the relief mechanism (V) through the injection valve (VII) of the extruder. The foam sheet is pulled and compressed into a three-roll polish stack (XI) and rolled up to form a foam sheet roll (XII).
[0007]
Thermoplastic polymers useful in the present invention include olefinic copolymers such as polyethylene, polypropylene, linear low density polyethylene, low density polyethylene, high density polyethylene, ethylene-octene copolymers, and at least 70% by weight vinyl aroma in the final resin. Polymers, copolymers, interpolymers and the like containing a group monomer as a monomer repeating unit are included. Non-limiting examples of vinyl aromatic monomers are described in US Pat. Nos. 4,666,987, 4,572,819 and 4,585,825.
[0008]
These preferred monomers have the formula:
Figure 0004787941
(Wherein R ′ is hydrogen or methyl, Ar is an aromatic ring structure having 1 to 3 aromatic rings, which may be substituted by alkyl, halogen or haloalkyl, where alkyl The group is a monomer having from 1 to 6 carbon atoms, haloalkyl means halogen-substituted alkyl, preferably Ar is phenyl or alkylphenyl, where alkylphenyl means alkyl-substituted phenyl group Phenyl is most preferred. Examples of typical vinyl aromatic monomers that can be used include all isomers of styrene, alphamethylstyrene, vinyltoluene, especially paravinyltoluene, all isomers of ethylstyrene, propylstyrene, vinyl. Biphenyl, vinyl naphthalene, vinyl anthracene and mixtures thereof. Group monomers may be combined with other copolymerizable monomers including, but not limited to, acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, acrylic acid, methyl acrylate, maleimide, phenyl maleimide The polymerization of vinyl aromatic monomers can also be carried out in the presence of pre-dissolved elastomers to produce impact modified or graft rubber containing products, which are described in US Pat. No. 3,123,655. No. 3,346,520, 3,639,522 and 4,409,369, particularly preferably high impact polystyrene resins. Blends and combinations of these can also be used.
[0009]
The blowing agent used in the method of the present invention is an appropriate physical blowing agent, and non-limiting examples thereof include carbon dioxide (CO 2 ), nitrogen (N 2 ), water (H 2 O), or combinations thereof. . In the present invention, these physical blowing agents may be defined as substantially 100% physical blowing agents in the absence of chemical blowing agents, even though they may contain small amounts of impurities and small amounts of other compounds. A preferred blowing agent is 100% carbon dioxide.
[0010]
The physical foaming agent can be used in an appropriate state, but is preferably a gas or a liquid. Carbon dioxide is preferably added as a liquid to the polymer melt. However, carbon dioxide gas can also be used in the present invention. Nitrogen and water can also be used in an appropriate state, but preferably nitrogen is added as a gas and water is added as a liquid. When two or more combinations or mixtures are used, typically separate metering systems are used to allow multiple streams to merge before the injection point of the cast-extrusion process. However, a plurality of blowing agents can be mixed in advance and injected using a single metering system.
[0011]
Additives such as pigments and / or nucleating agents may also be used in the method of the present invention. The addition of a nucleating agent is generally preferred and is preferably added from 0.001 to 10% by weight of the total polymer. A more preferable addition amount of the nucleating agent is 0.02 to 2% by weight. The nucleating agent is typically added to the polymer in an extruder. In one embodiment, the nucleating agent is talc.
[0012]
The method of the present invention can also utilize a coextrusion technique to produce a multilayer foam sheet. These multilayer sheets can optionally have one or more foam core layers or foam skin layers. For certain applications, it is desirable to have a combination of one or more foam core layers or skin layers and non-foam core layers or skin layers. For example, in one embodiment, a multilayer coextruded sheet is made of a foamed polystyrene core layer with an outer skin layer of non-foamed high impact polystyrene or non-foamed polystyrene resin / high impact polystyrene resin. Co-extrusion methods are well known in the art.
[0013]
Sheet extrusion is well known in the art and is published in 1988 by Hanser Publishers, New York. Hensen, Plastics Technology, Volume 7, pages 203-251 and Modern Plastics Encyclopedia Issue 66, No. 66, published in mid-October 1989. 11, pp. 256-257.
[0014]
In the sheet extrusion method used in the present invention, the polymer is fed to a sheet extruder and melted, whereupon the melt is transferred to an arbitrary feed block, and a single layer or multilayer extrudate (sheet) having a uniform thickness is passed through a die at the die outlet. To get. The foaming temperature at the die in the process of the present invention depends on the polymer to be foamed and is typically 150 ° C or higher, preferably 170-300 ° C. The polymer / blowing agent mixture is extruded into a low pressure region, preferably in air at atmospheric pressure, for foaming. The extruded foam sheet is drawn into a mechanism for pulling and compressing the foam extrudate so that a sheet of uniform thickness is obtained. One such mechanism is a rotatable and temperature controlled three roll polishing stack. In this mechanism, the sheet gauge is determined by the extrusion speed, roll stack spacing, line speed and draw ratio. The roll stack interval is the interval between the upper roll and the intermediate roll of the 3-roll polishing stack when used in the downward direction. The sheet gauge is monitored by equipment placed on a cartridge that moves perpendicular to the sheet direction and carries the gauge equipment across the sheet. Such gauge devices are well known in the art. The sheet exits these metering areas and moves over a series of guide rollers and is moved to the slit area and winder provided as needed or directly to the thermoforming process.
[0015]
The method of the present invention is also characterized in that the physical blowing agent is introduced into the polymer melt at a location prior to the die of the sheet extruder. Preferably, the foaming agent is injected through a one-way valve disposed in a compression release region (vent port) of an extrusion screw in the sheet extrusion line. If desired, a static mixer can be placed in front of the die to mix the polymer with the blowing agent and nucleating agent (if used). Foaming continues in the low pressure region as soon as the polymer melt mixture exits the die, just before the die exit. Typically, sheet foaming is used to extrude non-foamed materials or chemically foamed high density foam sheets. It has been found that by using a physical foaming agent and the above-described sheet extrusion line, a high-density foam sheet having improved gauge uniformity and density uniformity can be produced.
[0016]
The resulting foam sheet typically has a density in the range of 25-65 pounds / cubic foot (PCF) (400-1050 g / L (liter)), preferably 45-55 PCF (725-890 g / L). In other words, 0.04 to 1% by weight, preferably 0.04 to 0.5% by weight of a physical foaming agent is used per polymer weight. If less than 0.2% by weight of water is used in the process of the present invention, the water functions as a coolant and does not cause polymer expansion. This cooling effect is effective for controlling the foaming speed of the foam structure. When used in an amount greater than 0.2% by weight, foaming of the polymer melt mixture is observed. The cell dimension of the foam sheet in all directions is 1 mm or less, preferably 0.5 mm or less. The thickness of the foam sheet is preferably 0.1 to 3 mm.
[0017]
The resulting foam sheet has improved gauge uniformity and density uniformity. The gauge uniformity can be obtained by comparing the thickness of the final sheet at an appropriate position with respect to the average thickness of the final sheet. In comparison, the difference between the two thicknesses is less than 6%. The density uniformity can be obtained by comparing the density at an appropriate position of the final sheet with respect to the average sheet density of the final sheet. In comparison, the difference between the two densities is less than 4%. In other words, the gauge measured on the final sheet is nowhere different from 6% from the average sheet gauge, and the density measured on the final sheet is nowhere different from 4% from the average density.
[0018]
The following examples illustrate the invention. These examples are not intended to limit the scope of the invention. Amounts are given in weight percent unless otherwise noted.
[0019]
【Example】
Example 1:
A general-purpose polystyrene resin having a Mw of 320,000 was supplied to a sheet co-extrusion line having a high-pressure piston pump at the vent port position, and 100% CO 2 as a blowing agent was metered into the extrusion barrel. A static mixer was also placed at the end of the extruder to improve mixing of the polymer / blowing agent mixture. At the same time, a 50/50 blend of polystyrene resin and impact modified polystyrene resin was fed to another sheet extrusion line without blowing agent for the formation of a co-extruded solid skin layer. Polystyrene resin was foamed and coextruded with non-foamed polystyrene / HIPS blend to make a sheet with a foamed core resin and two solid skin layers adhered to both sides of the core resin layer. The sheet was pulled and compressed by a three roll polishing stack. The process conditions and sheet characteristics are shown in the following table.
[0020]
Figure 0004787941

[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of a sheet extrusion line used in the method of the present invention.

Claims (13)

溶融したモノビニリデン芳香族又はオレフィン系ポリマーを二酸化炭素、窒素、水又はそれらの組合せである物理発泡剤と接触させてシート押し出しライン内でポリマー／発泡剤混合物を形成し、この混合物をフラットシートダイを通じて低圧領域中に押し出して発泡させて発泡押し出し物をつくり、そしてこの発泡押し出し物を引っ張りそして圧縮して４００〜１０５０ｇ／Ｌの密度をもつ発泡体シートを形成することを特徴とする熱可塑性発泡体シートの製造方法。The molten monovinylidene aromatic or olefinic polymer is contacted with a physical blowing agent that is carbon dioxide, nitrogen, water, or a combination thereof to form a polymer / blowing agent mixture in the sheet extrusion line, and this mixture is formed into a flat sheet die. Thermoplastic foam characterized in that it is extruded through a low pressure region through a foam to produce a foam extrudate , and the foam extrudate is pulled and compressed to form a foam sheet having a density of 400-1050 g / L Manufacturing method of body sheet. 溶融したモノビニリデン芳香族ポリマーが用いられる請求項１の方法。  The process of claim 1 wherein a molten monovinylidene aromatic polymer is used. 物理発泡剤はシート押出機のダイの手前に備えられたワンウェイバルブを通じて液体の状態で溶融したポリマーに導入される請求項２の方法。 Physical blowing agent The method of claim 2 that will be introduced into the molten polymer in a liquid state through the one-way valve provided in front of the die of the sheet extruder. 溶融したオレフィン系ポリマーが用いられる請求項１の方法。  The process of claim 1 wherein a molten olefinic polymer is used. 溶融したオレフィン系ポリマーがポリエチレン、ポリプロピレン、線状低密度ポリエチレン、低密度ポリエチレン、高密度ポリエチレン、エチレン−オクテンコポリマー、又は最終樹脂中に少なくとも７０重量％のビニル芳香族モノマーをモノマー反復単位として含有させたオレフィン系コポリマー又はインターポリマーからなる請求項４の方法。  The molten olefinic polymer contains polyethylene, polypropylene, linear low density polyethylene, low density polyethylene, high density polyethylene, ethylene-octene copolymer, or at least 70% by weight vinyl aromatic monomer as monomer repeat unit in the final resin. The process of claim 4 comprising an olefinic copolymer or interpolymer. 溶融したオレフィン系ポリマーがポリプロピレンからなる請求項５の方法。  The method of claim 5, wherein the molten olefinic polymer comprises polypropylene. 発泡体の密度が７２５〜８９０ｇ／Ｌである請求項１の方法。The process of claim 1 wherein the density of the foam is 725-890 g / L. 均一な厚さが３ｍｍ未満である請求項１の方法。The method of claim 1 wherein the uniform thickness is less than 3 mm. 得られる発泡体シートは発泡体層及び少なくとも１層の非発泡体ポリマースキン層を備え、非発泡体ポリマースキン層の厚みは押し出されたシート厚みの約５０％である、請求項１の方法。The method of claim 1, wherein the resulting foam sheet comprises a foam layer and at least one non-foam polymer skin layer, wherein the thickness of the non-foam polymer skin layer is about 50% of the extruded sheet thickness. 請求項１の方法によって得られた発泡体シート。A foam sheet obtained by the method of claim 1. 最終シートの平均厚さに対する最終シートの適宜の位置の厚さの違いは６％より小さい、請求項１０の発泡体シート。The foam sheet of claim 10, wherein the difference in thickness at an appropriate location of the final sheet relative to the average thickness of the final sheet is less than 6%. 最終シートの平均シート密度に対する最終シートの適宜の位置の密度の違いは４％より小さい、請求項１０の発泡体シート。The foam sheet of claim 10, wherein the difference in density at an appropriate location of the final sheet relative to the average sheet density of the final sheet is less than 4%. 非発泡体ポリマースキン層を備える請求項１０〜１２のいずれか１項の発泡体シート。The foam sheet according to any one of claims 10 to 12, further comprising a non-foam polymer skin layer.
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